This invention relates to an electrostatic actuator in which an electrostatic force serves as the source of power.
Conventional electrical actuators mainly employ electromagnetic force as the source of driving power. However, since actuators of this type rely upon a permanent magnet or electromagnetic coil of great weight, the power density, which is the most important performance index of an actuator, is small. Furthermore, since a large current is required, a large amount of heat is generated.
Various electrostatic actuators have been proposed in order to solve these problems. With conventional electrostatic actuators, however, the following difficulties are encountered:
(a) The conventional electrostatic actuator has a stator and a slider, and an attractive force is produced between them. Consequently, it is difficult to achieve practical operation unless use is made of a mechanism for reducing frictional force. PA1 (b) A mechanism for maintaining an optimum spacing between the stator and the slider is required.
For these reasons, the conventional electrostatic actuator is of great weight and therefore the key advantage of an electrostatic actuator, namely the possibility of producing a large force with an actuator of light weight, cannot be exploited.
In an effort to eliminate these difficulties, the inventors of this application have previously proposed an electrostatic actuator that utilizes a film, as disclosed in the specification of Japanese Patent Application Laid-Open (KOKAI) No. 2-285978.
Further, an electrostatic actuator capable of solving the above-mentioned problems has been disclosed in a paper entitled "Electrostatic Film Actuator Prototype with Electrodes in both Stator and Slider" by T. Higuchi, S. Egawa, T. Niino and N. Nishiguchi, 1991 National Convention Record I.E.E. Japan, Section 7, April 1991, pp. 202-203 (in Japanese). Since this actuator iS operated by an electrostatic repulsive force produced between the stator and slider, the two problems mentioned above are solved. However, since this actuator is such that excitations of electrodes are changed over by switches, problems arise in that it is necessary to apply high DC voltages and in that a major part of the electrical energy supplied changes to heat within the switches, as a result of which efficiency is poor.
In another proposal, a closed-loop control-type electrostatic actuator having a position sensor is provided. The sensor employs current detectors connected to three-phase electrodes in the stator and four-phase high-frequency AC voltages connected to four-phase electrodes in the slider.
Thus, as set forth above, the electrostatic actuators of the prior art involve a number of problems, namely the problem of frictional force and the mechanism for eliminating it, the problem relating to the mechanism for maintaining the optimum spacing between the stator and slider, the problem of the large-scale auxiliary equipment needed for drive, such as the power supply, and such problems as the fact that a position sensor is needed, the driving force is too small and the energy efficiency is low.